Java TreeSet (med exempel)

I denna handledning lär vi oss om Java TreeSet-klassen och dess olika operationer och metoder med hjälp av exempel.

Den TreeSetklass av samlingar ramen för Java ger funktionaliteten hos en träddatastruktur.

Det utökar NavigableSet-gränssnittet.

Skapa en träduppsättning

För att skapa en träduppsättning måste vi först importera java.util.TreeSetpaketet.

När vi väl har importerat paketet, här är hur vi kan skapa en TreeSeti Java.

  TreeSet numbers = new TreeSet(); 

Här har vi skapat en TreeSetutan några argument. I det här fallet TreeSetsorteras elementen i naturligt (stigande ordning).

Vi kan dock anpassa sorteringen av element med hjälp av Comparatorgränssnittet. Vi lär oss om det senare i den här handledningen.

Metoder för TreeSet

I TreeSetklassen tillhandahåller olika metoder som tillåter oss att utföra olika operationer på apparaten.

Infoga element i TreeSet

• add() - infogar det angivna elementet i uppsättningen
• addAll() - infogar alla element i den angivna samlingen i uppsättningen

Till exempel,

 import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet evenNumbers = new TreeSet(); // Using the add() method evenNumbers.add(2); evenNumbers.add(4); evenNumbers.add(6); System.out.println("TreeSet: " + evenNumbers); TreeSet numbers = new TreeSet(); numbers.add(1); // Using the addAll() method numbers.addAll(evenNumbers); System.out.println("New TreeSet: " + numbers); ) ) 

Produktion

 TreeSet: (2, 4, 6) New TreeSet: (1, 2, 4, 6) 

Åtkomst till TreeSet-element

För att komma åt elementen i en träduppsättning kan vi använda iterator()metoden. För att kunna använda den här metoden måste vi importera java.util.Iteratorpaketet. Till exempel,

 import java.util.TreeSet; import java.util.Iterator; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(2); numbers.add(5); numbers.add(6); System.out.println("TreeSet: " + numbers); // Calling iterator() method Iterator iterate = numbers.iterator(); System.out.print("TreeSet using Iterator: "); // Accessing elements while(iterate.hasNext()) ( System.out.print(iterate.next()); System.out.print(", "); ) ) ) 

Produktion

 TreeSet: (2, 5, 6) TreeSet med Iterator: 2, 5, 6, 

Ta bort element

• remove() - tar bort det angivna elementet från uppsättningen
• removeAll() - tar bort alla element från uppsättningen

Till exempel,

 import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(2); numbers.add(5); numbers.add(6); System.out.println("TreeSet: " + numbers); // Using the remove() method boolean value1 = numbers.remove(5); System.out.println("Is 5 removed? " + value1); // Using the removeAll() method boolean value2 = numbers.removeAll(numbers); System.out.println("Are all elements removed? " + value2); ) ) 

Produktion

TreeSet: (2, 5, 6) Är 5 borttagen? true Är alla element borttagna? Sann

Metoder för navigering

Eftersom TreeSetklassen implementeras NavigableSetger den olika metoder för att navigera över elementen i träduppsättningen.

1. första () och sista () metoder

• first() - returnerar det första elementet i uppsättningen
• last() - returnerar det sista elementet i uppsättningen

Till exempel,

 import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(2); numbers.add(5); numbers.add(6); System.out.println("TreeSet: " + numbers); // Using the first() method int first = numbers.first(); System.out.println("First Number: " + first); // Using the last() method int last = numbers.last(); System.out.println("Last Number: " + last); ) ) 

Produktion

 TreeSet: (2, 5, 6) Första siffran: 2 Senaste numret: 6 

2. tak (), golv (), högre () och lägre () Metoder

• högre (element) - Returnerar det lägsta elementet bland de element som är större än det angivna element.
• lower (element) - Returnerar det största elementet bland de element som är mindre än det angivna element.
• tak (element) - Returnerar det lägsta elementet bland de element som är större än det angivna elementet. Om elementet passerat finns i en träduppsättning returnerar det det elementskickade som ett argument.
• golv (element) - Returnerar det största elementet bland de element som är mindre än det angivna element. Om elementet passerat finns i en träduppsättning returnerar det det elementskickade som ett argument.

Till exempel,

 import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(2); numbers.add(5); numbers.add(4); numbers.add(6); System.out.println("TreeSet: " + numbers); // Using higher() System.out.println("Using higher: " + numbers.higher(4)); // Using lower() System.out.println("Using lower: " + numbers.lower(4)); // Using ceiling() System.out.println("Using ceiling: " + numbers.ceiling(4)); // Using floor() System.out.println("Using floor: " + numbers.floor(3)); ) ) 

Produktion

 TreeSet: (2, 4, 5, 6) Använda högre: 5 Använda nedre: 2 Använda tak: 4 Använda golv: 2 

3. Metoder för pollfirst () och pollLast ()

• pollFirst() - returnerar och tar bort det första elementet från uppsättningen
• pollLast() - returnerar och tar bort det sista elementet från uppsättningen

Till exempel,

 import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(2); numbers.add(5); numbers.add(4); numbers.add(6); System.out.println("TreeSet: " + numbers); // Using pollFirst() System.out.println("Removed First Element: " + numbers.pollFirst()); // Using pollLast() System.out.println("Removed Last Element: " + numbers.pollLast()); System.out.println("New TreeSet: " + numbers); ) ) 

Produktion

 TreeSet: (2, 4, 5, 6) Removed First Element: 2 Removed Last Element: 6 New TreeSet: (4, 5) 

4. headSet(), tailSet() and subSet() Methods

headSet(element, booleanValue)

The headSet() method returns all the elements of a tree set before the specified element (which is passed as an argument).

The booleanValue parameter is optional. Its default value is false.

If true is passed as a booleanValue, the method returns all the elements before the specified element including the specified element.

For example,

 import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(2); numbers.add(5); numbers.add(4); numbers.add(6); System.out.println("TreeSet: " + numbers); // Using headSet() with default boolean value System.out.println("Using headSet without boolean value: " + numbers.headSet(5)); // Using headSet() with specified boolean value System.out.println("Using headSet with boolean value: " + numbers.headSet(5, true)); ) ) 

Output

 TreeSet: (2, 4, 5, 6) Using headSet without boolean value: (2, 4) Using headSet with boolean value: (2, 4, 5) 

tailSet(element, booleanValue)

The tailSet() method returns all the elements of a tree set after the specified element (which is passed as a parameter) including the specified element.

The booleanValue parameter is optional. Its default value is true.

If false is passed as a booleanValue, the method returns all the elements after the specified element without including the specified element.

For example,

 import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(2); numbers.add(5); numbers.add(4); numbers.add(6); System.out.println("TreeSet: " + numbers); // Using tailSet() with default boolean value System.out.println("Using tailSet without boolean value: " + numbers.tailSet(4)); // Using tailSet() with specified boolean value System.out.println("Using tailSet with boolean value: " + numbers.tailSet(4, false)); ) ) 

Output

 TreeSet: (2, 4, 5, 6) Using tailSet without boolean value: (4, 5, 6) Using tailSet with boolean value: (5, 6) 

subSet(e1, bv1, e2, bv2)

The subSet() method returns all the elements between e1 and e2 including e1.

The bv1 and bv2 are optional parameters. The default value of bv1 is true, and the default value of bv2 is false.

If false is passed as bv1, the method returns all the elements between e1 and e2 without including e1.

If true is passed as bv2, the method returns all the elements between e1 and e2, including e1.

For example,

 import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(2); numbers.add(5); numbers.add(4); numbers.add(6); System.out.println("TreeSet: " + numbers); // Using subSet() with default boolean value System.out.println("Using subSet without boolean value: " + numbers.subSet(4, 6)); // Using subSet() with specified boolean value System.out.println("Using subSet with boolean value: " + numbers.subSet(4, false, 6, true)); ) ) 

Output

 TreeSet: (2, 4, 5, 6) Using subSet without boolean value: (4, 5) Using subSet with boolean value: (5, 6) 

Set Operations

The methods of the TreeSet class can also be used to perform various set operations.

Union of Sets

To perform the union between two sets, we use the addAll() method. For example,

 import java.util.TreeSet;; class Main ( public static void main(String() args) ( TreeSet evenNumbers = new TreeSet(); evenNumbers.add(2); evenNumbers.add(4); System.out.println("TreeSet1: " + evenNumbers); TreeSet numbers = new TreeSet(); numbers.add(1); numbers.add(2); numbers.add(3); System.out.println("TreeSet2: " + numbers); // Union of two sets numbers.addAll(evenNumbers); System.out.println("Union is: " + numbers); ) ) 

Output

 TreeSet1: (2, 4) TreeSet2: (1, 2, 3) Union is: (1, 2, 3, 4) 

Intersection of Sets

To perform the intersection between two sets, we use the retainAll() method. For example,

 import java.util.TreeSet;; class Main ( public static void main(String() args) ( TreeSet evenNumbers = new TreeSet(); evenNumbers.add(2); evenNumbers.add(4); System.out.println("TreeSet1: " + evenNumbers); TreeSet numbers = new TreeSet(); numbers.add(1); numbers.add(2); numbers.add(3); System.out.println("TreeSet2: " + numbers); // Intersection of two sets numbers.retainAll(evenNumbers); System.out.println("Intersection is: " + numbers); ) ) 

Output

 TreeSet1: (2, 4) TreeSet2: (1, 2, 3) Intersection is: (2) 

Difference of Sets

To calculate the difference between the two sets, we can use the removeAll() method. For example,

 import java.util.TreeSet;; class Main ( public static void main(String() args) ( TreeSet evenNumbers = new TreeSet(); evenNumbers.add(2); evenNumbers.add(4); System.out.println("TreeSet1: " + evenNumbers); TreeSet numbers = new TreeSet(); numbers.add(1); numbers.add(2); numbers.add(3); numbers.add(4); System.out.println("TreeSet2: " + numbers); // Difference between two sets numbers.removeAll(evenNumbers); System.out.println("Difference is: " + numbers); ) ) 

Output

 TreeSet1: (2, 4) TreeSet2: (1, 2, 3, 4) Difference is: (1, 3) 

Subset of a Set

To check if a set is a subset of another set or not, we use the containsAll() method. For example,

 import java.util.TreeSet; class Main ( public static void main(String() args) ( TreeSet numbers = new TreeSet(); numbers.add(1); numbers.add(2); numbers.add(3); numbers.add(4); System.out.println("TreeSet1: " + numbers); TreeSet primeNumbers = new TreeSet(); primeNumbers.add(2); primeNumbers.add(3); System.out.println("TreeSet2: " + primeNumbers); // Check if primeNumbers is subset of numbers boolean result = numbers.containsAll(primeNumbers); System.out.println("Is TreeSet2 subset of TreeSet1? " + result); ) ) 

Output

 TreeSet1: (1, 2, 3, 4) TreeSet2: (2, 3) Is TreeSet2 subset of TreeSet1? True 

Other Methods of TreeSet

Method	Description
clone()	Creates a copy of the TreeSet
contains()	Searches the TreeSet for the specified element and returns a boolean result
isEmpty()	Checks if the TreeSet is empty
size()	Returns the size of the TreeSet
clear()	Removes all the elements from the TreeSet

To learn more, visit Java TreeSet (official Java documentation).

TreeSet Vs. HashSet

Both the TreeSet as well as the HashSet implements the Set interface. However, there exist some differences between them.

• Unlike HashSet, elements in TreeSet are stored in some order. It is because TreeSet implements the SortedSet interface as well.
• TreeSet provides some methods for easy navigation. For example, first(), last(), headSet(), tailSet(), etc. It is because TreeSet also implements the NavigableSet interface.
• HashSet is faster than the TreeSet for basic operations like add, remove, contains and size.

TreeSet Comparator

In all the examples above, tree set elements are sorted naturally. However, we can also customize the ordering of elements.

For this, we need to create our own comparator class based on which elements in a tree set are sorted. For example,

 import java.util.TreeSet; import java.util.Comparator; class Main ( public static void main(String() args) ( // Creating a tree set with customized comparator TreeSet animals = new TreeSet(new CustomComparator()); animals.add("Dog"); animals.add("Zebra"); animals.add("Cat"); animals.add("Horse"); System.out.println("TreeSet: " + animals); ) // Creating a comparator class public static class CustomComparator implements Comparator ( @Override public int compare(String animal1, String animal2) ( int value = animal1.compareTo(animal2); // elements are sorted in reverse order if (value> 0) ( return -1; ) else if (value < 0) ( return 1; ) else ( return 0; ) ) ) ) 

Output

 TreeSet: (Zebra, Horse, Dog, Cat) 

In the above example, we have created a tree set passing CustomComparator class as an argument.

CustomComparator-klassen implementerar Comparatorgränssnittet.

Vi åsidosätter sedan compare()metoden. Metoden sorterar nu element i omvänd ordning.

För att lära dig mer, besök Java Comparator (officiell Java-dokumentation).